Do you just trace the initials in Royal icing to stick on a buttercream cake?

or with candy melts or chocolate

I used a candy mold to form my Monograms on a wedding cake.
But I used the mold to form fondant initials for adhering to a fondant cake. In the case of buttercream, I would use white chocolate.

couturiere, that is a beautiful cake! The monogram is perfect!